Driving apparatus for speed changing and steering of a vehicle

ABSTRACT

A driving apparatus ( 2 ) for speed changing and steering of a vehicle consists of a first driving unit ( 21 ) for speed changing in advancing and reversing and a second driving unit ( 22 ) for steering, which are arranged in a longitudinal row and are attached to a vehicle chassis ( 12 ). Each of the first driving unit ( 21 ) and the second driving unit ( 22 ) has a common structure, which comprises a housing and an HST and left and right differential output shafts contained in the housing. A left first differential output shaft ( 40 L) and a left second differential output shaft ( 44 L) are connected with each other so as to be rotated in the same direction, and a right first differential output shaft ( 40 R) and a right second differential output shaft ( 44 R) are connected with each other so as to be rotated in opposite directions. Both first and second HSTs of the first driving unit ( 21 ) and a second driving unit ( 22 ) receives power from engine ( 11 ) through a common single belt ( 30 ). A movable swash plate ( 57 ) of a hydraulic pump ( 51 ) of the first HST is connected to a speed change pedal ( 15 ) and a movable swash plate ( 76 ) of a hydraulic pump ( 71 ) of the second HST is connected to a steering wheel ( 14 ).

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a driving apparatus for speedchanging and steering of a vehicle comprising a pair of hydrostatictransmissions (hereinafter referred to as HSTs) for driving a pair ofleft and right axles, wherein one of the pair is used for steering andthe other is used for speed changing in advancing and reversing.

[0003] 2. Related Art

[0004] U.S. Pat. No. 4,782,650, for example, describes a vehicleprovided with a pair of HSTs, which are disposed in a lateral row andare connected with each other, and left and right axles projectingrespectively from the pair of the HSTs laterally outwardly. Drivingwheels are fixed respectively onto utmost ends of the axles. The leftand right axles are driven respectively by changing operation ofslanting angles of movable swash plates of the pair of HSTs.

[0005] The left and right axles are driven at the same speed by the pairof HSTs in case of straight advancing and reversing. They are driven atdifferent speeds in case of steering.

[0006] However, because the above mentioned conventional vehicle uses adifferent HST to drive each axle, it can advance or reverse straightonly when the output rotational speeds of the pair of the HSTs areequal. Thus, each of the HSTs needs to be adjusted with respect to itsoutput speed for a long time while in operation. Additionally, accuracyis required to produce parts of the HSTs to minimize different outputsbetween them. For example, if there is a difference in volume betweenhydraulic pumps or motors of the pair of the HSTs, feelings both inturning left and right are different from each other, thus the vehiclebecomes hard to control.

[0007] Additionally, the above-described conventional vehicle islaterally wide because of the pair of HSTs are laterally disposedbetween the left and right driving wheels.

[0008] Furthermore, a speed changing operating tool, such as a speedchange pedal, is connected respectively to both output regulatingmembers of the pair of HSTs. A steering operating tool, such as asteering wheel, is also connected to both HSTs. This results incomplicated linkages between the speed changing operating tool and theboth output regulating members, and between the steering operating tooland the both output regulating members. Thus, the cost for production ofthe linkages and the space required for them in the vehicle areincreased. These linkages also require a more complicated control systemfor a steering wheel and a speed changing pedal.

[0009] Other conventional vehicles control steering using steered frontwheels. These vehicles, however, have a large turning radius which isinefficient when operating in crowded areas. For example, when mowinglawn near trees, steered front wheels are inefficient because it takesseveral passes in order to complete the area adjacent to a single tree.

SUMMARY OF THE INVENTION

[0010] A first object of the present invention is to provide a compact,low production cost driving apparatus for speed changing and steering ofa vehicle including a pair of similarly structured driving units, eachof which comprises a housing, an HST, a differential gear unit drivinglyconnected with the HST, and a pair of differential output shafts,enabling a vehicle provided with the driving apparatus to be operated ina straight line without requiring adjustment to equalize the output ofboth driving units and to have a small turning radius.

[0011] To achieve the first object, the driving apparatus consists of afirst driving unit for speed changing in advancing and reversing of thevehicle, which integrally includes a first HST driven by a prime moverand a pair of left and right projecting differential output shaftsdrivingly connected with the first HST. The driving apparatus alsoincludes a second driving unit for steering of the vehicle, whichintegrally includes a second HST driven by the prime mover and a pair ofleft and right projecting differential output shafts drivingly connectedwith the second HST. A pair of drive trains are interposed between eachof the first and second differential output shafts. One of the drivetrains drivingly connects the left first and left second output shaftswith each other, the other drivingly connects the right first and rightsecond output shafts with each other, so that the first and seconddifferential output shafts connected by one of the two drive trains arerotated in the same direction with respect to each other and the otherfirst and second differential output shafts connected by the other drivetrain are rotated in opposite directions with respect to each other.

[0012] In such a construction, an output regulating member of the firstHST is connected with a speed changing operating tool, such as a footpedal, to be used for speed changing in advancing and reversing. Drivingwheels are attached to the first differential output shafts. The outputregulating member of the second HST is connected with a steeringoperating tool, such as a steering wheel, to be used for steering.

[0013] Accordingly, the vehicle can spin or turn at a small radius.Also, the first differential output shafts projecting laterally from thesingle first driving unit can be used as left and right driving axles,so that the left and right axles do not need to be adjusted to equalizetheir speed, thereby simplifying the work when operating the vehicle inforward or reverse. Additionally, in a vehicle with multiple wheels,only the differential drive of the pair of driving wheels attached tothe first differential output shafts is required for steering, therebyallowing a vehicle with multiple wheels to have simple driven wheels.

[0014] The speed of advancing and reversing of the vehicle can besteplessly changed by operation of the speed changing operating tool(the foot pedal) easily because of the stepless output regulation of thefirst HST. The vehicle can also be steered smoothly and easily byoperation of the steering operating tool (the steering wheel) because ofthe stepless output regulation of the second HST.

[0015] The linkage between the speed changing operating tool and theoutput regulating member of the first HST and the linkage between thesteering operating tool and the output regulating member of the secondHST are simple and compact. These linkages are compactly disposed belowan operator's deck.

[0016] The first and second driving units are attached to a vehiclechassis so as to be juxtaposed in either front or rear of each other,thereby enabling the vehicle provided with the driving apparatus to belaterally narrow. Thus, the vehicle can be compact and can have a verysmall turning circle in addition to the above mentioned drive trains.

[0017] With regard to the transmitting mechanism between an output shaftof the prime mover and the input shafts of the first and second HSTs ofthe first and second driving units, the output shaft is disposed betweenthe input shafts of the first and second HST. Pulleys fixed onto theoutput shaft of the prime mover and the two input shafts of the firstand second HSTs are bound with a single belt. Accordingly, the spacerequired for the transmitting mechanism is small, thereby allowing for amore compact vehicle and the cost of production thereof is reducedbecause due to the use of a single belt.

[0018] The prime mover is an engine having a vertically axialcrankshaft. The output shaft of the engine is vertically axiallydisposed such that the transmitting mechanism is between the outputshaft of the engine and the input shafts of the first and second HSTs.

[0019] Furthermore, a cutting deck is provided to the vehicle with adriving apparatus of the present invention. The vehicle can spin or turnat a small radius beside or among trees or buildings, thereby enablingthe lawn mowing to be performed efficiently.

[0020] A second object of the present invention is to provide a compact,low production cost driving apparatus for speed changing and steering ofa vehicle including a pair of similar HSTs and a pair of similardifferential output gear units which are separated from but drivinglyconnected with their respective HST, enabling the vehicle provided withthe driving apparatus to be oiperated in a straight line withoutrequiring adjustment to equalizing output of both left and right axles,and to have a small turning circle.

[0021] To achieve the second object, the driving apparatus comprises afirst HST driven by a prime mover, a first differential gear unit and apair of left and right first differential output shafts for the purposeof speed changing in advancing and reversing. The driving apparatus alsocomprises a second HST driven by the prime mover, a second differentialgear unit and a pair of left and right second differential output shaftsfor the purpose of steering. A pair of drive trains are interposedbetween the first and second differential output shafts, wherein one ofthe drive trains drivingly connects the left first and left secondoutput shafts with each other, the other drive train drivingly connectsthe right first and second output shafts with each other, such that thefirst and second differential output shafts connected by one of the twodrive trains are rotated in the same direction with respect to eachother and the other first and second differential output shaftsconnected by the other drive train are rotated in opposite directionswith respect to each other.

[0022] An HST unit and a differential gear unit separate from each otherare widely produced at low cost because of their simple structures, sothat the driving apparatus constructed by assembly of them can bereduced in cost.

[0023] In such a construction, the output regulating member of the firstHST is connected with a speed changing operating tool, such as a footpedal, to be used for speed changing in advancing and reversing. Drivingwheels are attached to the first differential output shafts. The outputregulating member of the second HST is connected with a steeringoperating tool, such a steering wheel, to be used for steering.

[0024] Accordingly, the vehicle can spin or turn at a small radius.Also, the first differential output shafts projecting laterally from thesingle first differential gear unit can be used as left and rightdriving axles, so that the left and right axles do not need to beadjusted to equalize their speed, thereby simplifying the work whenoperating the vehicle in forward or reverse. Additionally, in a vehiclewith multiple wheels, only the differential drive of the pair of drivingwheels attached to the first differential output shafts is required forsteering, thereby allowing a vehicle with multiple wheels to have simpledriven wheels.

[0025] The speed of advancing and reversing of the vehicle can besteplessly changed by operation of the speed changing operating tool(the foot pedal) easily because of the stepless output regulation of thefirst HST. The vehicle can be steered smoothly and easily by operationof the steering operating tool (the steering wheel) because of thestepless output regulation of the second HST.

[0026] The linkage between the speed changing operating tool and theoutput regulating member of the first HST and the linkage between thesteering operating tool and the output regulating member of the secondHST are simple and compact. These linkages are compactly disposed belowan operator's deck.

[0027] With regard to the transmitting mechanism between an output shaftof the prime mover and the input shafts of the first and second HSTs ofthe first and second driving units, the output shaft is disposed betweenthe input shafts of the first and second HST. Pulleys fixed onto theoutput shaft of the prime mover and the two input shafts of the firstand second HSTs are bound with a single belt. Accordingly, the spacerequired for the transmitting mechanism is small, thereby allowing for amore compact vehicle and the cost of production thereof is reducedbecause due to the use of a single belt.

[0028] The prime mover is an engine having a vertically axialcrankshaft. The output shaft of the engine is vertically axiallydisposed such that the transmitting mechanism is between the outputshaft of the engine and the input shafts of the first and second HSTs.

[0029] Furthermore, a cutting deck is provided to the vehicle with adriving apparatus of the present invention. The vehicle can spin or turnat a small radius beside or among trees or buildings, thereby enablingthe lawn mowing to be performed efficiently.

[0030] These and other objects of the invention will become moreapparent in the detailed description and examples which follows.

BRIEF DESCRIPTION OF THE FIGURES

[0031]FIG. 1 is a side view showing an entire lawn mower provided with adriving apparatus of the present invention;

[0032]FIG. 2 is a plan view of a pair of driving units disposed in alongitudinal row;

[0033]FIG. 3 is a right side view of a pair of driving units disposed ina longitudinal row;

[0034]FIG. 4 is a left side view a pair of driving units disposed in alongitudinal row;

[0035]FIG. 5 is a sectional plan view a pair of driving units disposedin a longitudinal row;

[0036]FIG. 6 is a diagram of a power transmitting system of the drivingapparatus;

[0037]FIG. 7 is a side view showing another entire lawn mower providedwith the driving apparatus of the present invention, wherein a seat ismounted above the driving apparatus;

[0038]FIG. 8 is a side view showing another entire lawn mower providedwith the driving apparatus of the present invention, wherein a cuttingdeck is provided in front of the vehicle thereof, and

[0039]FIG. 9 is a diagram of a power transmitting system of anotherdriving apparatus of the present invention comprising a pair of drivingunits, wherein each driving unit includes an HST unit and andifferential gear unit separated from each other.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0040] As best seen in FIG. 1, the overall construction of a lawn mower1 provided with a driving apparatus of the present invention will beexplained.

[0041] A front column 13 is provided upright on a front portion of avehicle chassis 12. A steering wheel 14 as a steering operating toolprojects upwardly from front column 13. A speed change pedal 15 andbrake pedals (not shown) are disposed beside front column 13. A pair offront wheels 16 are disposed respectively on both lateral sides of thefront lower portion of vehicle chassis 12. Front wheels 16 are casterwheels, so that they can be horizontally rotated smoothly so as to berapidly oriented toward the aiming direction when the vehicle turns bydifferential driving of left and right driving wheels. Thus, the feelingin steering of the vehicle can be improved. A single front wheel 16 ormore than two front wheels 16 may be also used.

[0042] A seat 17 is mounted on a center portion of vehicle chassis 12. Adeck portion 12 a is formed as an operator's footboard on an upper endof vehicle chassis 12 in the vicinity of a front of seat 17. A cuttingdeck 9 (a mower) is disposed below deck portion 12 a. Cutting deck 9comprises a casing 19 provided therein with at least one rotary blade,which is driven by power from an engine 11 through pulleys, belt and thelike. Cutting deck 9 is suspended at front and rear portions of itscasing 19 by linkages which are vertically movable.

[0043] Engine 11 is mounted on a rear portion of vehicle chassis 12 andis covered with a bonnet. Engine 11 has a vertically axial crankshaftprovided with a vertically downwardly projecting output shaft 11 a. Anoutput pulley 20 is fixed onto a lower end of output shaft 11 a.

[0044] A driving apparatus 2 of the present invention is disposed on thelower rear portion of vehicle chassis 12. As shown in FIGS. 2, 3 and 4,driving apparatus 2 consists of a first driving unit 21 for speedchanging in advancing and reversing and a second driving unit 22 forsteering, which contain substantially similarly constructed hydrostatictransmissions (HSTs), respectively. Second driving unit 22 is preferablydisposed in rear of first driving unit 21. They are oriented inlongitudinally opposite directions and are fixed to vehicle chassis 12.Second driving unit 22 alternatively may be disposed in front of firstdriving unit 21.

[0045] A first input shaft 25 projects from a housing 23 of firstdriving unit 21 and a second input shaft 26 projects from a housing 24of second driving unit 22. A first input pulley 27 and a fan 39 is fixedonto first input shaft 25 and a second input pulley 28 and another fan39 is fixed onto second input shaft 26. Output pulley 20 and a tensionpulley 29 are disposed in a space between first and second input pulleys27 and 28. All the pulleys 20, 27 and 28 are tied together with a singlebelt 30, so that first and second input shafts 25 and 26 can receive thepower of engine 11 simultaneously. Tension pulley 29 is pushed againstbelt 30.

[0046] Another pulley 31 is fixed onto first input shaft 25. A supportboss 32 is provided upright on a longitudinal intermediate of vehiclechassis 12. A counter shaft 33 rotatably penetrates support boss 32. Forthe purpose of driving of cutting deck 9, pulleys 34 and 35 are fixedonto both upper and lower ends of counter shaft 33, and a belt 36 areinterposed between pulleys 31 and 34. A belt tension clutch may bedisposed between pulleys 35 and 38, thereby enabling cutting deck 9 tobe drivingly switched on and off.

[0047] A pair of first differential output shafts (axles) 40L and 40Rproject respectively from both lateral sides of housing 23 of firstdriving unit 21. Sprockets 41L and 41R are fixed respectively onto firstdifferential output shafts 40L and 40R. Rear wheels 43 are fixedrespectively onto first differential output shafts 40L and 40R so as tobe disposed outside of sprockets 41L and 41R, respectively.

[0048] With respect to the conventional vehicle provided with a pair ofdriving units disposed in lateral row, left and right driving axles areindependently driven by the pair of driving units, which are separatedfrom each other, thereby requiring output of the driving units to beequalized for straight advancing and reversing of the vehicle. However,the vehicle of the present invention is constructed so that the left andright axles constituted by first differential output shafts 40L and 40Rare differentially connected with each other by a single differentialgear unit within housing 23 of first driving unit 21, thereby requiringno adjustment to equalize the output of the axles.

[0049] Vehicle 1 turns substantially around either rear wheel 43. Asshown in FIG. 7, seat 17 may also be disposed just above firstdifferential output shafts 40L and 40R. This places seat 17 verticallyin line with rear wheels 43, thereby reducing the force on an operatorwhen vehicle 1 is turned or spun.

[0050]FIG. 8 shows an alternative arrangement of vehicle 1 in whichcutting deck 9 is disposed in front of the vehicle body. In thisarrangement, driving wheels 43 are located in the front of vehicle 1 andcaster wheels 16 are at the rear of vehicle 1. Such a constructionallows cutting deck 9 to cut the grass before any wheels have presseddown the grass. Also, vehicle 1 can mow easily with respect to a placewhich the vehicle body cannot enter, for example, a place beneathbranches of a tree, because forwardly projecting cutting deck 9 canenter such a place.

[0051] Returning to FIGS. 2, 3 and 4, a pair of second differentialoutput shafts (steering driving shafts) 44L and 44R project respectivelyfrom both lateral sides of housing 24 of second driving unit 22.Sprockets 45L and 45R are fixed respectively onto second differentialoutput shafts 44L and 44R.

[0052] At one of the lateral sides (at a left side in this embodiment)of housings 23 and 24, a chain 46 is interposed between sprockets 41Land 45L. At the other side (right side in this embodiment), a sprocket47 is disposed behind sprocket 45R and is rotatably supported onto ashaft 48 projecting laterally from vehicle chassis 12, and a chain 49 isinterposed between sprockets 4IR and 47.

[0053] Sprocket 45R engages at its lower end with chain 49. Thus, ifsecond differential output shafts 44L and 44R rotates in the samerotational direction when both first differential output shafts 40L and40R are neutral, sprockets 45L and 45R are rotated in the samerotational direction, so that first differential output shafts 40L and40R are rotated in the opposite rotational directions. Gears, gears andshafts, belts and pulleys or the like may be used in place of thesprockets and chains for the purpose of power transmitting between firstand second driving units 21 and 22.

[0054] Next, explanation will be given on inner structures of first andsecond driving units 21 and 22, in accordance with FIGS. 5 and 6.

[0055] Housings 23 and 24 of first and second driving units 21 and 22are similarly constructed. Each of housings 23 and 24 contains an HST, adifferential gear unit, a drive train between the HST and thedifferential gear unit, and a pair of differential output shafts, allwhich comprise common components and are similarly structured.

[0056] At first, first driving unit 21 will be described. Housing 23,which consists of vertically divided halves separably joined with eachother, contains a first HST, first differential output shafts 40L and40R and a drive train drivingly connecting first HST with differentialoutput shafts 40L and 40R. First HST comprises a L-like shaped centersection 51 having a horizontal pump mounting surface and a verticalmotor mounting surface, a hydraulic pump 52 mounted onto the horizontalpump mounting surface and a hydraulic motor 53 mounted onto the verticalmotor mounting surface. Hydraulic motor 53 is disposed in front ofhydraulic pump 52. Hydraulic pump 52 and hydraulic motor 53 are fluidlyconnected with each other through a closed fluid circuit formed withincenter section 51.

[0057] Housing 23 is constructed so that vertically divided halves arejoined at their flat surrounding joint surfaces with each other along ahorizontal joint plane. Bearing portions for a motor shaft 54 and acounter shaft 55 are provided on their joint surfaces, so that motorshaft 54 and counter shaft 55 are rotatably supported with their axesdisposed on the horizontal joint plane. Bearing portions for rotatablysupporting first differential output shafts 40L and 40R areeccentrically disposed above the horizontal joint plane. Firstdifferential output shafts 40L and 40R are differentially connected witheach other through a differential gear unit 56 and respectively projectat their utmost end portions laterally outwardly from the left and rightoutside ends of housing 23.

[0058] Hydraulic pump 52 is mounted on the horizontal pump mountingsurface of center section 51. In this regard, an input shaft 25 as apump shaft is vertically disposed along the axis of hydraulic pump 52. Acylinder block is anchored to input shaft 25 and is rotatably andslidably mounted on the horizontal pump mounting surface. A plurality ofpistons are reciprocally movably inserted into the cylinder blockthrough biasing springs. The heads of the pistons abut against a movableswash plate 57. Thus, by slanting operation of movable swash plate 57 asa output regulating member, the amount and direction of oil dischargedfrom hydraulic pump 52 can be changed.

[0059] For the purpose of slanting operation of movable swash plate 57,a control shaft 59 is pivoted onto a side wall of housing 23 in parallelwith first differential output shaft 40. A neutral spring 61 for biasingmovable swash plate 57 to its neutral position is fitted around aportion of control shaft 59 within housing 23, so as to enable itsneutral position to be adjusted. A control arm 60 is fixed onto aportion of control shaft 59 out of housing 23 and is connected to aspeed changing operating tool like a lever or a pedal through a link 62and the like.

[0060] In this embodiment, the speed changing operating tool is speedchange pedal 15. Speed change pedal 15 is pivoted at its longitudinallymiddle portion so that vehicle 1 advances by treading the front halfportion of speed change pedal 15 and reverses by treading the rear halfportion thereof. The speed of advancing and reversing of the vehicle canbe steplessly controlled in proportion to degree of rotation of speedchange pedal 15 by treading thereof. Speed change pedal 15 is shownconstructed like a seesaw, but may alternatively be divided into twopedals. Other constructions can also replace it for a speed changingtool.

[0061] Link 62 is compactly disposed substantially longitudinally belowdeck portion 12 a. In a conventional driving apparatus also comprised apair of driving units with each used for both speed changing andsteering, the speed changing operating tool, such as a pedal, requiredcomplicated connections to output regulating members of both HSTs unitsthrough a complicated linkage, for example a pair of links. Speed changepedal 15 of driving apparatus 2 of the present invention, to thecontrary, is connected to only single control arm 60 through only singlelink 62, because only movable swash plate 57 of first driving unit 21 isused as an output regulating member for speed changing. Thus, vehicle 1can be constructed more compactly and at a reduced cost.

[0062] In such a construction, control arm 60 is rotated along thelongitudinal direction of the vehicle by rotational operation of speedchange pedal 15 and movable swash plate 57 is slanted by rotation ofcontrol shaft 59, so that the amount and direction of operating oildischarged from hydraulic pump 52.

[0063] The pressure oil from hydraulic pump 52 is charged into hydraulicmotor 53 through oil passages bored within center section 51. Hydraulicmotor 53 comprises a cylinder block 63 rotatably slidably mounted ontothe vertical motor mounting surface of center section 51. A plurality ofcylinder holes are bored in cylinder block 63 and a plurality of pistons64 are reciprocally movably inserted into the cylinder holes throughbiasing springs, respectively. Pistons 64 abut at their head against afixed swash plate 65. Motor shaft 54 is horizontally disposed along therotational axis of cylinder block 63 and is not relatively rotatablyanchored to cylinder block 63. Hydraulic motor 53 is just soconstructed.

[0064] Motor shaft 54 is provided thereon with a brake unit 66. A gear67 is fixed onto an end portion of motor shaft 54. Gear 67 engages witha large diametric gear 68 fixed onto counter shaft 55. A small diametricgear 69 also fixed onto counter shaft 55 engages with a ring gear 70 ofdifferential gear unit 56. Differential gear unit 56 is driven in statethat ring gear 70 is rotated at reduced speed by the power transmittedfrom motor shaft 54, thereby driving left and right first differentialoutput shafts 40L and 40R.

[0065] Second driving unit 22, which is disposed in a longitudinallyopposite direction as first driving unit 21, similarly comprises housing24 and a second HST including a hydraulic pump 71 and a hydraulic motor72 contained in housing 24. A control shaft 73 for rotating a movableswash plate 76 of hydraulic pump 71 projects leftwardly from housing 24.A control arm 74 is fixed onto a portion of control shaft 73 out ofhousing 24 and is connected to steering wheel 14 through a link 75 andthe like. Link 75 is compactly disposed substantially longitudinallybelow deck portion 12 a. As shown in FIG. 6, a pinion 77 is fixed onto abasic portion of a stem of steering wheel 14 and engages with afan-shaped gear 78. Gear 78 is connected with link 75. Thus, byrotational operation of steering wheel 14, gear 78 engages with pinion77 and is rotated at reduced speed, so as to rotate movable swash plate76 through link 75.

[0066] Similar to the simplified construction described above for link62 interposed between speed change pedal 15 and control arm 60, steeringwheel 14 as a steering operating tool is simply connected to only singlecontrol arm 74 through single link 75 because only movable swash plate76 of second driving unit 22 is used as an output regulating member forsteering. As opposed to the complex linkages required for a steering andspeed changing in a conventional system wherein each is connected to twolaterally disposed HSTs which independently drive left and right axles,the linkages for steering and for speed change in accordance with thepresent invention are simplified, compact, and reduced in cost, therebycontributing to providing a compact vehicle at low cost.

[0067] Next, explanation will be given on controlling operation of avehicle provided with driving apparatus 2 of the present invention soconstructed as the above mentioned. When engine 11 is driven, inputshafts 25 and 26 are always driven. For the purpose of straightadvancing or reversing, steering wheel 14 is set in state of straightmoving, so that second driving unit 22 is neutral. In this condition,movable swash plate 57 of first driving unit 21 is rotated by forward orrearward tread of speed change pedal 15. Thus, first differential outputshafts 40L and 40R are driven at even speed, so that the vehicleadvances or reverses.

[0068] When steering wheel 14 is rotated for steering in state that thevehicle is advancing or reversing, movable swash plate 76 of seconddriving unit 22 is rotated so that hydraulic motor 72 is driven, therebydriving second differential output shafts 44L and 44R. If motor shaft 54is rotated in its regular direction, sprocket 45 on right seconddifferential output shaft 44R is reversely rotated. Thus, only leftsecond differential output shaft 44L is regularly rotated bydifferential operation of differential gear unit 79, therebytransmitting an accelerating power to left first differential outputshaft 40L, so that vehicle 1 turns right. If steering wheel 14 isrotated so as to rotate motor shaft 54 in reverse direction, vehicle 1turns left.

[0069] When speed change pedal 15 is not trod, hydraulic pump 51 offirst driving unit 21 is neutral. Then, if steering wheel 14 is rotated,movable swash plate 76 of second driving unit 22 is rotated so as todrive hydraulic motor 72. When second differential output shafts 44L and44R are rotated in regular direction, left first differential outputshaft 40L is rotated in advancing direction and right first differentialoutput shaft 40R is rotated in reverse direction, so that vehicle 1spins rightwardly. If steering wheel 14 is rotated so as to rotatesecond differential output shafts 44L and 44R in reverse direction,vehicle 1 spins leftwardly.

[0070] Driving apparatus 2 uses a pair of common structured drivingunits 21 and 22, each of which comprises an HST, a differential gearunit, a drive train between the HST and the differential gear unit and apair of differential output shafts, one for speed changing in advancingand reversing and the other for steering, so that a common driving unitof the generally conventional structure can be used for the twodifferent purposes, thereby reducing cost.

[0071] In another embodiment of the present invention, as shown in FIG.9, driving apparatus 2′ comprises a pair of a first driving system 21′for speed changing in advancing and reversing and a second drivingsystem 22′ for steering. Driving system 21′ is constructed so that afirst HST unit 80 and a first differential gear unit 81, which isseparated from first HST unit 80 (that is, not contained within ahousing of first HST unit 80), are drivingly connected with each otherby a drive train such as a gear train, a chain and sprockets, belt andpulleys or the like. Second driving system 22′ comprising a second HSTunit 82 and a second differential gear unit 83 is similarly constructed,so that second differential gear unit 83 is separated from second HSTunit 82.

[0072] Each of first and second HST units 80 and 82 comprises a housingand a hydraulic pump P and a hydraulic motor M, both of which arefluidly connected with each other, contained in the housing and disposedso that an input shaft Pa as a pump shaft of hydraulic pump P isvertically axially oriented and an output shaft Ma as a motor shaft ofhydraulic motor M is horizontally laterally axially oriented. Each offirst and second differential gear units 81 and 83 is disposed so thatits respective input member (not shown), such as a gear, a sprocket, apulley or the like is horizontally laterally axially disposed. Thus,each of the driving trains such as a gear train, a chain, a belt or thelike is interposed longitudinally, vertically or longitudinallyslantingly between output member Ma and the input member.

[0073] Each of differential gear units 81 and 83 is provided with leftand right differential output shafts. Left and right first differentialoutput shafts 40L and 40R as axles project laterally from both lateralsides of first differential gear unit 81. Left and right seconddifferential output shafts 44L and 44R as driving shafts for steeringproject laterally from both lateral sides of second differential gearunit 83. The drive trains between left first and left seconddifferential output shafts 40L and 44L and between right first and rightsecond differential output shafts 44L and 44R are structured similarlywith those of the above mentioned driving apparatus 2. In this regard,the left drive train between left differential output shafts 40L and 44Lcomprises chain 46 and sprockets 41L and 45L and the right drive trainbetween right differential output shafts 40R and 44R comprises chain 49and sprockets 41R, 45R and 47, so that left and right drive trains areso constructed as to be rotated in opposite directions to each other.Each of the drive trains may be replaced by a gear train, a belt andpulleys or the like.

[0074] In such an alternative embodiment, there are an HST unit and adifferential gear unit independent to each other, which are widelyproduced. Each of the HST unit and the differential gear unit can beobtained at low cost because of its simple structure. Thus, drivingapparatus 2′ can be constructed at low cost by assembly of generallyavailable HST units and differential gear units.

[0075] The previously described structures of driving apparatus 2 suchas the linkage connecting movable swash plates of first and second HSTunits 80 and 82 respectively to speed change pedal 15 and steering wheel14, the transmitting mechanism from output pulley 20 of engine 11 toinput pulleys 25 and 26 of first and second HSTs through single belt 30,the attachment of cutting deck 19 and other constructions can besimilarly applied to driving apparatus 2′.

What is claimed is:
 1. A driving apparatus for speed changing andsteering of a vehicle, comprising: a first driving unit integrallyprovided with a first HST connected with a prime mover and a pair ofleft and right first differential output shafts driven by said firstHST, wherein said first driving unit is attached to a vehicle chassis; asecond driving unit integrally provided with a second HST connected withsaid prime mover and a pair of left and right second differential outputshafts driven by said second HST, wherein said second driving unit isattached to said vehicle chassis; a drive train drivingly connectingsaid left first output shaft and said left second output shaft with eachother, and a drive train drivingly connecting said right first outputshaft and said right second output shaft with each other, wherein one ofsaid first and second differential output shafts connected by one ofsaid two drive trains are rotated in the same direction and the other ofsaid first and second differential output shafts connected by the otherof said drive trains are rotated in opposite directions.
 2. A drivingapparatus for speed changing and steering of a vehicle as set forth inclaim 1 , wherein said second driving unit is juxtaposed in either frontor rear of said first driving unit.
 3. A driving apparatus for speedchanging and steering of a vehicle as set forth in claim 1 , furthercomprising: a output regulating member of said first HST connected witha speed changing operating tool provided on said vehicle.
 4. A drivingapparatus for speed changing and steering of a vehicle as set forth inclaim 3 , wherein said speed changing operating tool is a foot pedal. 5.A driving apparatus for speed changing and steering of a vehicle as setforth in claim 3 , wherein said output regulating member of said firstHST is connected with said speed changing operating tool by a speedcontrol linkage disposed below an operator's deck.
 6. A drivingapparatus for speed changing and steering of a vehicle as set forth inclaim 1 , further comprising: a output regulating member of said secondHST connected with a steering operating tool provided on said vehicle.7. A driving apparatus for speed changing and steering of a vehicle asset forth in claim 6 , wherein said steering operating tool is asteering wheel.
 8. A driving apparatus for speed changing and steeringof a vehicle as set forth in claim 6 , wherein said output regulatingmember of said second HST is connected with said steering operating toolby a steering control linkage disposed below an operator's deck.
 9. Adriving apparatus for speed changing and steering of a vehicle as setforth in claim 1 , further comprising: driving wheels attachedrespectively to said left and right first differential output shafts.10. A driving apparatus for speed changing and steering of a vehicle asset forth in claim 9 , wherein said vehicle chassis is provided at thelongitudinally opposite portion thereof to said driving wheels with atleast one caster wheel.
 11. A driving apparatus for speed changing andsteering of a vehicle as set forth in claim 1 , further comprising: anoutput shaft of said prime mover interposed between an input shaft ofsaid first HST and an input shaft of said second HST.
 12. A drivingapparatus for speed changing and steering of a vehicle as set forth inclaim 11 , further comprising: pulleys fixed respectively onto saidinput shafts of said first and second HSTs and said output shaft of saidprime mover, wherein said pulleys are bound with a single belt for powertransmission.
 13. A driving apparatus for speed changing and steering ofa vehicle as set forth in claim 12 , wherein said prime mover is anengine provided with a crankshaft having a vertical rotational axis. 14.A driving apparatus for speed changing and steering of a vehicle as setforth in claim 1 , wherein said vehicle has a cutting deck.
 15. Adriving apparatus for speed changing and steering of a vehicle,comprising: a first HST connected with a prime mover; a firstdifferential gear unit separated from said first HST and drivinglyconnected with said first HST, wherein said first differential gear unitis provided with a pair of left and right first differential outputshafts; a second HST connected with said prime mover; a seconddifferential gear unit separated from said second HST and drivinglyconnected with said second HST, where in said second differential gearunit is provided with a pair of left and right second differentialoutput shafts; a drive train drivingly connecting said left first outputshaft and said left second output shaft with each other, and a drivetrain drivingly connecting said right first output shaft and said rightsecond output shaft with each other, wherein said first and seconddifferential output shafts connected by one of said two drive trains arerotated in the same direction and the other first and seconddifferential output shafts connected by the other of said drive trainsare rotated in the opposite directions.
 16. A driving apparatus forspeed changing and steering of a vehicle as set forth in claim 15 ,further comprising: a output regulating member of said first HSTconnected with a speed changing operating tool provided on said vehicle.17. A driving apparatus for speed changing and steering of a vehicle asset forth in claim 16 , wherein said speed changing operating tool is afoot pedal.
 18. A driving apparatus for speed changing and steering of avehicle as set forth in claim 16 , wherein said output regulating memberof said first HST is connected with said speed changing operating toolby a speed control linkage disposed below an operator's deck.
 19. Adriving apparatus for speed changing and steering of a vehicle as setforth in claim 15 , further comprising: a output regulating member ofsaid second HST connected with a steering operating tool provided onsaid vehicle.
 20. A driving apparatus for speed changing and steering ofa vehicle as set forth in claim 19 , wherein said steering operatingtool is a steering wheel.
 21. A driving apparatus for speed changing andsteering of a vehicle as set forth in claim 19 , wherein said outputregulating member of said second HST is connected with said steeringoperating tool by a steering control linkage disposed below anoperator's deck.
 22. A driving apparatus for speed changing and steeringof a vehicle as set forth in claim 15 , further comprising: drivingwheels attached respectively to said first differential output shafts.23. A driving apparatus for speed changing and steering of a vehicle asset forth in claim 22 , wherein said vehicle chassis is provided at thelongitudinally opposite portion thereof to said driving wheels with atleast one caster wheel.
 24. A driving apparatus for speed changing andsteering of a vehicle as set forth in claim 15 , further comprising: anoutput shaft of said prime mover interposed between an input shaft ofsaid first HST and an input shaft of said second HST.
 25. A drivingapparatus for speed changing and steering of a vehicle as set forth inclaim 24 , further comprising: pulleys fixed respectively onto saidinput shafts of said first and second HSTs and said output shaft of saidprime mover, wherein said pulleys are bound with a single belt for powertransmission.
 26. A driving apparatus for speed changing and steering ofa vehicle as set forth in claim 25 , wherein said prime mover is anengine provided with a crankshaft having a vertical rotational axis. 27.A driving apparatus for speed changing and steering of a vehicle as setforth in claim 15 , wherein said vehicle has a cutting deck.